Intestinal mucosal lymphatic permeability: An electron microscopic study of endothelial vesicles and cell junctions

In order to determine the route of passage of water-soluble macromolecules across lacteals of intestinal villi of mice and guinea pigs, peroxidase, ferritin, and chylomicrons were used as tracers. Saline-injected animals served as control. Lacteal junctions were classified as close junctions, tight junctions, open junctions, and indeterminate junctions. In lacteals there were 10 close junctions, 89 tight junctions, 6 open junctions, and 149 indeterminate junctions. Ferritin and peroxidase were frequently identified within pinocytotic vesicles. Peroxidase (diameter about 50 Å) was seen within close junctions but did not appear to penetrate tight junctions. Ferritin (diameter about 110 Å) did not penetrate tight or close junctions. Chylomicrons (diameter about 2000 Å) did not penetrate close or tight junctions, were occasionally seen in large vesicles, and were often identified within overlapping endothelial cell processes. These data suggest that the major route of transport of these substances across lacteals of the intestinal mucosa is vesicular rather than through endothelial cell junctions.